A conventional actuator is operated in response to an applied voltage potential to perform some mechanical operation such as a valve operation or a pump operation. The state of the actuator can be changed by an applied voltage and a driving current through the actuator in a forward or reverse direction. Such bi-directional current flow is necessary for normal operation. As illustrated in FIG. 1A, one such actuator can be an electrochemical pump actuator that is operated in response to an applied voltage potential.
As illustrated in FIG. 1A, an electrochemical pump-type actuator can comprise a housing containing therein at least three chambers wherein the first and second chambers contain a pumping fluid, and the third chamber contains a substance to be pumped from an outlet of the third chamber. In operation, an applied voltage +V is used to move pumping fluid from chamber one into chamber two through a selective membrane between chambers one and two, thereby exerting pressure on chamber three through expansion of the expansion diaphragm between chambers two and three. The contents of chamber three are then forced or pumped from chamber three through the exit port as indicated by the arrow in FIG. 1A. Reversal of the applied voltage potential −V is then used to reverse the movement of the pumping fluid from chamber two into chamber one, thereby creating a reduced pressure in chamber three by a reverse movement of the expansion diaphragm. Content is then drawn into chamber three and the process is repeated. Further details of an exemplary electrochemical pump can be found in U.S. Pat. No. 7,718,047; U.S. Pat. No. 8,187,441; and U.S. Pat. No. 8,343,324, the entire content of all of which are expressly incorporated herein by reference.
A number of valves are required for such pumping operations, and the operation of such valves must be coordinated with the pumping operations. For example, an intake valve can be provided to allow content from a source to enter chamber three. The intake valve can then be closed and an outlet valve opened and the pump actuated to allow the pumped content from chamber three to reach a destination. The outlet valve can then be closed and the intake valve opened and the pump deactivated to allow content from the source to enter chamber three. The intake valve can then be closed and the outlet valve again opened and the pump actuated to allow the pumped content from chamber three to reach the destination. The operation can be repeated as necessary to pump content using the electrochemical pump actuator.
The states of the valves and pump can be changed by an applied voltage and a driving current through the actuator of each in a forward or reverse direction. One such method to do so is the use of a standard H-bridge driving circuit. As shown in FIG. 1B, a standard H-bridge driving circuit can consist of two half-bridges and is used to control a single driven device D. Such a circuit allows a voltage Vin to be applied across a driven device D in either direction. The term “H-bridge” is derived from the graphical representation of such a circuit, which typically includes four switches. When the switches S1 and S4 are closed and switches S2 and S3 are open, a positive voltage can be applied across the device load D. By opening switches S1 and S4 and closing switches S2 and S3, the voltage is reversed across the device load D. Such conventional H-bridge driving circuits can be constructed as integrated circuits or can be built from discrete components.
However, in some applications, the overall design of the system is highly space and cost constrained, and any opportunity to reduce the overall number of components is helpful. Accordingly, there is a need to provide such driving circuits that perform in a manner associated with a conventional H-bridge driving circuit, but which reduce the required space and cost of the driving circuit.